The prevention and reversal of digoxin intoxication with specific antibodies

Kinetics of the Fab fragments of digoxin antibodies and of bound digoxin in patients with severe digoxin intoxication

17 patients with severe digoxin intoxication were successfully treated with 320 to 480 mg Fab fragments of digoxin-specific IgG from sheep. The infusion period ranged between 0.5 and 7 h. Serum and urine concentrations of digoxin bound to Fab fragments, and in 11 cases unbound Fab fragments in serum, were determined during and after the infusion. The renal clearance of bound digoxin and therefore of the antibody was 13.6 ml/min. The median extrarenal clearance of the Fab fragments was 10.9 ml/min. The half-life of the serum concentrations starting at 12 h was 14.3 h, and the value was increased to 25.4 h when regression began at 24 h; the corresponding apparent distribution volumes were 25.9 and 541. These figures exceed the volume of the extracellular space and suggest intracellular penetration of the Fab fragments. The dosage of the antibody should be sufficiently high to bind digoxin in the most severe cases of poisoning. The maximum serum concentrations of bound antibody were 30 mg/l after 3 h and 20 mg/l after 5 h. A loading dose of 160 mg followed by an infusion of 0.5 mg/min was sufficient to absorb digoxin re-diffusing into the serum during the first 8 h. In some cases free digoxin reappeared in the serum 8-12 h after beginning the treatment. This might be prevented by infusing a further ampoule at a rate of 0.1 mg/min or less.

The effect of immunization with digoxin-specific antibodies on digoxin disposition in the mouse

After intravenous dosing, digoxin was rapidly distributed to tissues, with a distribution half-life of 3.0 min. The highest digoxin concentrations at 1 hr post dosing were found in lymph nodes, adrenals, gallbladder (including contents), liver and kidney respectively. Digoxin concentrations in the heart, spleen, brain, lung, skeletal muscle and fat were similar to, or lower than, those in the plasma. The apparent volume of distribution (AVd) was 1 l/kg, and the plasma elimination half-life and clearance (Cl) 2.8 hr and 0.25 l/kg per hr respectively. When digoxin was given one day after passive immunization with digoxin-specific immunoglobulin G (IgG) or Fab fragments the respective plasma digoxin concentrations were elevated some 26- and 5-fold respectively compared with control values. Consequently there were reductions in AVd (93 and 32%) and Cl (94 and 50%). The effect of IgG treatment on clearance was still apparent when the hapten was given up to 14 days after immunization, while the weaker effect of Fab-treatment was less persistent. Although tissue digoxin concentrations were slightly lower in the immunised mice, it was only in the lymph nodes at 10 and 14 days after IgG treatment that the reduction in hapten concentration was statistically significant.

Digoxin-specific antibody fragments and a calcium antagonist for reversal of digoxin-induced mesenteric vasoconstriction

The effect of digoxin-specific antibody fragments on glycoside-induced mesenteric vasoconstriction were investigated. Digoxin caused a sustained contraction of strips of isolated feline mesenteric artery lasting for several hours, while in anaesthetized cats it produced a significant decrease in blood flow and increase in resistance in the mesenteric artery. In-vitro, digoxin's contractile effect was inhibited by 'prophylactic' addition of antibody to the organ bath, but the clinical use for prophylaxis is not a practical proposition. When the antibodies were added with the contraction of the arterial strip in response to digoxin already established, the tone of the preparation decreased significantly over 3 h, but the effect of the glycoside was not fully reversible. In-vivo, control animals not treated with antibodies developed arrhythmias, mesenteric blood flow fell by more than 50% and resistance increased by more than 80% relative to the initial values. These animals died of ventricular fibrillation before the end of the experiment. Animals treated with digoxin-specific antibody fragments after receiving digoxin injections showed no further decrease in mesenteric blood flow and 90 min after the last dose of digoxin, the flow was recovering and mesenteric resistance decreasing. Furthermore, all the animals that had received antibodies remained in sinus rhythm to the end of the experiment. In view of the latent period to onset of action of the antibodies, valuable time may be lost in impaired mesenteric blood flow. To bridge the gap or, indeed, as primary treatment, calcium antagonists merit consideration; in our experiments mesenteric vasoconstriction was abolished within a few minutes by application of the dihydropyridine calcium antagonist 4-(2,1,3-benzo-oxadiazol-4-yl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylic aid, diethyl ester (PY 108-068).

Suicidal digoxin poisoning: conventional treatment and antibody therapy

A 66-year-old mand suffering from severe coronary heart disease took digoxin with suicidal intent an was treated for the ensuing complete atrioventricular block with digoxin-specific antibody fragments. Two and a half hours after intravenous infusion of the antibody fragments, the signs of intoxication passed off, and atrial fibrillation with a normal ventricular rate was reinstated. Antibody therapy is capable of permanently abolishing the signs of symptoms of digitalis poisoning after a matter of hours. Such a rapid or complete response cannot be achieved by any conventional form of treatment. This advantage must be weighed against the risks (immunologic reactions, loss of the therapeutic effect of the cardiac glycoside if an overdose of antibody is given). Moreover, antibody therapy does not take effect immediately, as is understandable in view of the mechanism of action. It should therefore be instituted in good time in potentially life-threatening cases of intoxication.

Extracellular versus intracellular digoxin action on bovine myocardium, using a digoxin antibody and intracellular glycoside application

1. The actions of externally and internally applied digoxin in heart ventricular muscle have been compared. 2. External application of digoxin (5 x 10(-8)--10(-7) M) had an inotropic effect, a steady level of twitch tension being reached at the end of about 3 hr. 3. Addition of an anti-digoxin antibody to the bathing solution prevented or reversed the digoxin effect, depending on the time of application. 4. The efflux of the antibody-[3H]digoxin-complex could be fitted by a single exponential with a half-time of 18 min. 5. In the absence of antibody, [3H]digoxin washout was two-compartmental with half-times of 4 and 72 min respectively. It is thought that the fast process signifies efflux from the extracellular space while the slow process reflects the washout of initially membrane bound glycoside. 6. When digoxin was applied by a cut end method, there was no effect on contractile strength. 7. The profile of radioactivity several hours following exposure to [3H]digoxin clearly indicated movement from cell to cell, the concentration of [3H]digoxin being above 10(-7) M in half the preparation at the end of 6 hr. Longitudinal diffusivity averaged 8.6 x 10(-8) cm-2 sec-1. 8. We conclude that digoxin has an inotropic effect when reaching the surface membrane of cardiac cells from the outside but is ineffective when applied from the inside.

Acute, massive poisoning with digitoxin: report of seven cases and discussion of treatment

Severe digitoxin poisoning in seven patients is reported. Doses taken varied from 2 to 20 mg, and maximal plasma concentrations of digitoxin from 50 to 237 nmol/L. One patient died from ventricular fibrillation, and the course in another was considerably protracted due to severe complications. The course in all patients was more dependent on underlying heart disease than on the plasma digitoxin concentration. Based on our own experiences and survey of the literature the following treatment is proposed: Gastric aspiration and lavage followed by instillation of activated charcoal should even be performed many hours after drug intake. In order to interrupt the enterohepatic circulation of digitoxin, repeated doses of charcoal should be given. Charcoal is preferable to cholestyramine because of its better tolerability. Ventricular arrhythmias should not be treated unless they are serious, because most antiarrhythmic drugs may further impede the AV-conduction. Phenytoin is the drug of choice, because the AV-conduction is less affected or even improved, and because the metabolism of digitoxin is accelerated. Conduction disturbances with bradycardia are frequently seen and may occur suddenly. Prophylactic introduction of a transvenous pacing catheter is therefore recommended as a routine procedure.

The effectiveness of digoxin-specific F(ab')2-antibody fragments in the treatment of digitoxin poisoning: experimental investigations in the cat

In animal experiments heterologous digoxin-specific F(ab')2 antibody fragments have been found to be effective for the treatment of arrhythmias induced by toxic doses of digoxin. So far they have been successfully employed in three patients suffering from digoxin poisoning. The present study was undertaken to test whether these antibodies are also effective in the treatment of digitoxin poisoning. Ventricular tachycardia, induced in digitalized cats by intravenous injections of digitoxin, was fatal in four out of five controls. However, sinus rhythm was reinstated in all the animals treated with digoxin-specific F(ab')2 after onset of the arrhythmia. Cross-reactivity between the antibodies used and digitoxin, while slight in vitro, is, nevertheless, sufficient to justify their clinical use in cases of digitoxin poisoning.

Treatment of a case of lanatoside C intoxication with digoxin-specific F(ab')2 antibody fragments

In animal experiments arrhythmias induced by cardiac glycosides which prove fatal if untreated can be terminated by administration of glycoside-specific antibodies. Immunotherapy with digoxin-specific antibody fragments had hitherto only been employed on one occasion, namely in a person who had taken a massive overdose of digoxin with suicidal intent and who had failed to respond to symptomatic treatment. The present paper describes the use of F(ab')2 fragments of digoxin-specific antibodies in a female patient with lanatoside C intoxication to treat the associated life-threatening cardiac arrhythmia. The arrhythmia was rapidly terminated and normal sinus rhythm was restored. Treatment with the heterologous antibodies did not cause any side-effects.